This invention relates in general to annular seals that resiliently engage the outer surfaces of cylindrical shafts to prevent passage of oil or other fluids therethrough when such shafts are rotated during use. In particular, this invention relates to an improved method and apparatus for measuring irregularities that are formed on the outer surface of a cylindrical shaft during manufacture so as to determine whether such irregularities would create a preferential lead when the shaft is rotated during use.
Annular seal assemblies are well known structures that are adapted to engage the outer surface of a rotatable shaft so as to prevent a fluid (such as oil) from passing therethrough when the shaft is rotated during use. One commonly known type of annular seal assembly is a radial lip seal assembly. A typical radial lip seal assembly includes a rigid outer annular case that is press fit within an opening formed through a housing of a machine or mechanism. An annular sealing element is secured to the case and extends radially inwardly into sealing engagement with an outer circumferential surface of a rotatable shaft. The radial lip seal assembly is designed to prevent the fluid from passing axially therethrough from one side thereof to the other side thereof as the shaft is rotated during use.
Traditionally, it has been believed to be desirable to form the outer circumferential surface of such a shaft to be perfectly smooth and concentrically located relative to the radial lip seal assembly. Such a perfectly smooth and concentrically oriented outer circumferential surface would allow for a smooth and uninterrupted engagement of the radially extending portion of the sealing element therewith so as to provide a fluid-tight engagement. However, as a practical matter, the outer circumferential surface of the shaft is never perfectly smooth, but rather has a variety of irregularities formed therein during manufacture. Furthermore, at least in some instances, the presence of some of such irregularities has been found to be desirable because they provide small recesses that can retain fluid therein. Such fluid can function as a lubricant to minimize the adverse effects of friction and heat that would otherwise be generated at the sealing element when the shaft is rotated during use.
It has been found that if the irregularities are relatively small in size and sufficiently randomly distributed over the outer circumferential surface of the shaft, then their presence will not likely affect the operation of the radial lip seal assembly. However, if such irregularities are relatively large or are not sufficiently randomly distributed over the outer circumferential surface of the shaft, then their presence may advantageously or adversely affect the operation of the radial lip seal assembly. Such an affect can occur when the irregularities are sized and oriented in such a manner as to function in the manner of a helical thread formed in the outer circumferential surface of the shaft, referred to herein as a preferential lead. It is known that such a helical thread or preferential lead, when oriented in the correct direction, can advantageously function with the sealing element to resist fluid leaking therethrough by essentially pumping it back to the fluid side of the radial lip seal assembly. It is also known, however, that such a helical thread or preferential lead, when oriented in the incorrect direction, can adversely function against the sealing element to promote fluid leakage by pumping it through to the air side of the radial lip seal assembly. Thus, to insure that the radial lip seal assembly functions satisfactorily, it has been found to be important to determine whether the outer circumferential surface of the shaft possesses a preferential lead and, if so, in which direction such preferential lead is oriented.
Unfortunately, the size and orientation of the irregularities formed in the outer circumferential surface of the shaft are so small as to be not visible to the naked eye or otherwise readily ascertainable. The traditional method of determining the magnitude and direction of the preferential lead is to hang a pair of weights on opposite sides of the shaft by means of a thin thread, and then rotate the shaft. If a preferential lead is present on the shaft, the thread and the weights will be move in an axial direction along the shaft. The direction and speed of such movement is indicative of the magnitude and direction of the preferential lead. Although effective, this method has been found to be time consuming and imprecise. Accordingly, it would be desirable to provide an improved method and apparatus for measuring the irregularities on the outer circumferential surface of a cylindrical shaft to determine whether such irregularities create a preferential lead when the shaft is rotated during use and, if so, in which direction such preferential lead is oriented.
This invention relates to an improved method and apparatus for measuring the irregularities on the outer circumferential surface of a cylindrical shaft to determine whether such irregularities create a preferential lead when the shaft is rotated during use. An apparatus, such as an interferometric measuring device, is used to obtain qualitative information regarding a first portion of the outer circumferential surface of the shaft. That qualitative information can be used to generate a two dimensional or three dimensional visual representation of a first portion of the outer circumferential surface of the shaft. Then, the shaft is rotated by a predetermined amount, and the apparatus is again used to generate a visual representation of a second portion of the outer circumferential surface of the shaft. This process is repeated as necessary to obtain a plurality of visual representations that together span across a predetermined amount, fifteen degrees, for example, of the outer circumferential surface of the shaft. The size of this circumferential span may be selected as desired. Following this acquisition, the plurality of visual representations are processed by an image processor so as to generate a single comprehensive enlarged visual representation of a relatively large surface area of the outer circumferential surface of the shaft. The enlarged visual representation is preferably shaded, colored, or otherwise highlighted to illustrate the irregularities that are formed in the relatively large surface area of the outer circumferential surface of the shaft. The single comprehensive enlarged visual representation can be analyzed to determine whether such irregularities create a preferential lead when the shaft is rotated during use and, if so, in which direction such preferential lead is oriented.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.